Method and apparatus for controlling feed to shaft furnace



T. F. REED Aug. 21, 1962 METHOD AND APPRATUS FOR CONTROLLING FEED T0SHAFT FURNACE Filed June 23, 1959 N @uw INVENTOR. 77/0/1/45 F. @50

are

3,050,299 METTI-101) AND APPARATUS FOR CNTROLLING FEED Tt) SHAFT FURNACEThomas F. Reed, Pittsburgh, Pa., assigner to United States SteelCorporation, a corporation of New .ersey Filed .lune 23, 1959, Ser. No.822,298 2 Claims. (Cl. 263-29) or disk and then heat the balls to thepoint of incipient fusion in a shaft furnace. The balls feed to the topof the furnace, attain a maximum temperature in a combustion zone a fewinches below the stocklne, and discharge from the bottom. The usualfeeding means includes a conveyor whose discharge end continuallytraverses the furnace above the stockline and deposits balls over thewhole area. Typical conveyor arrangements for this purpose are shown inDavis Patent No. 2,757,782 and De Vaney et al. Patent No. 2,834,484.

Desirably the combustion zone remains at a uniform constant level, butin practice its level tends to deviate non-uniformly. To correct suchdeviations the traversing drive for the conveyor commonly is equippedwith a speed control device which causes the discharge end of theconveyor to dwell over some spots on the burden and pass quickly overothers. Previously known means through which the speed control devicereceives its intelligence include a mechanical feeler, as shown in DeVaney et al. Patents Nos. 2,792,132 and 2,834,484, or a temperaturemeasuring device, as shown in Sisco Patent No. 2,739,800. A feelersenses the level of the stockline profile and causes the conveyor todwell over low spots and pass quickly over high spots. A temperaturemeasuring device senses the temperature of combustion gases fromdifferent spots on the burden and causes the conveyor to dwell over hotspots and pass quickly over cool spots. Thus the feeler tends tomaintain a level stockline, and the temperature measuring device auniform combustion gas temperature, but I have observed neither affornsexactly the form of control that is needed.

An object of the present invention is to provide an improved method andapparatus for controlling feed of material to a shaft furnace in whichcontrol is effected in accordance with the relative permeability of thefurnace burden to fiow of gases.

A further object is to provide an improved method and apparatus forcontrolling the traversing drive of a conveyor which feeds a shaftfurnace whereby the discharge end of the conveyor dwells over spots inthe furnace burden of high permeability and passes quickly over spots oflow permeability.

A more specific object is to provide an improved control method andapparatus of the foregoing type in which the velocity of combustion gasat different spots over the burden is measured with an anemometer or theequivalent, the temperature at these spots is measured with athermocouple or the equivalent, these measurements are combined tofurnish an indication of gas velocity at a standard temperature, andthis indication is used to effect control of the traversing drive.

In the drawing:

FIGURE l is a diagrammatic vertical sectional View of the upper portionof a shaft furnace whose feed means is equipped with a control apparatusin accordance with my invention; and

FIGURE 2 is a schematic diagram of an electric circuit suitable for usein my apparatus.

FIGURE l shows the upper portion of a conventionall shaft furnace 10 forindurating balled iron ore fines. The

furnace can be either rectangular or circular in cross sec-v tion, andits feed means can lbe of any suitable type for traversing the top, forexample as shown in the afore-v mentioned patents. For purposes ofillustration, the feed means is shown diagrammatically as including aconveyor belt 12, a movable carriage 13 on which the belt is mounted, afixed support 14 for the carriage, and a. variable speed traversingdrive motor 15. Preferably the furnace has a hood 16 above its feedmeans and a stack 17 above the hood. The furnace wall has a suitablycurtained opening for admitting the feed means, as known in the art. Thefeed means feeds balls to the furnace where they form a burden B. Air isintroduced to the' and escape through the stack. The burden has theusuall combustion zone C.

ln accordance with the present invention, carriage 13` carries ananemometer 18 and a thermocouple 19 positioned over the burden Badjacent the spot to which con-V veyor 12 discharges balls. As theconveyor traverses the furnace, the anemometer measures the velocity atwhich combustion gases pass through the burden at each spot andgenerates a voltage proportionate thereto. thermocouple measures thetemperature of these gases and generates another voltage proportionateto this temperature. The latter voltage is used to compute the velocityof combustion gases at a standard temperature (32 F.). The permeabilityof the bed below the spot where velocity is measured is of coursedirectly proportional to the velocity at standard temperature. Both theanemometer and the thermocouple per se are conventional instruments;hence they are not shown in detail.

' The gas velocity at standard temperature can be computed bymultiplying the anemometer reading lby the ratio where Tis thetemperature indicated by the thermocouple. FIGURE 2 shows schematicallyone form of circuit for accomplishing this computation. The anemometer18 and thermocouple 19 transmit voltages proportionate to the velocityand temperature to conventional voltage amplifiers 20 and 21respectively. These amplifiers are equipped with volume controls 22 and23, which are adjusted manually to place the voltage outputs of the twoampliers on scale. The negative output terminals of both amplifiers areelectrically connected to one end of a potentiometer slide wire 24. Abias voltage source 28 is connected between the negative output terminalof amplifier 21 and the slide wire to furnish a voltage proportionate tothe term 460 of the foregoing ratio. The positive output terminal ofamplifier 21 is electrically connected to the other end of this slidewire. The positive output terminal of amplifier 20 is electricallyconnected to the arm 25 of the potentiometer through a conventionalself-balancing device 26. Thus a voltage proportionate t-o the absolutetemperature (460-I-T) is applied across the full length of the slidewire 24 and a voltage proportionate to the anemometer reading across avariable portion of the slide wire determined by the position of arm 25.When the circuit balances, no current flows from amplifier 20. Theself-balancing device 26 and arm 25 are mechanically connected asindicated by a dotted line 29, whereby the self-balancing deviceautomatically positions arm 25 to balance the circuit in this way. Withproper calibration, the position of the arm when the circuit is inbalance indicates the relative permeability of the burden.

FIGURE 2 also shows schematically one form of speed Patented Aug. 21,1962` The control device for the traversing drive motor 15. This deviceincludes a second potentiometer 27 in the iield circuit of this motor.The arm of potentiometer 27 is mechanically linked to arm 25, asindicated by a dotted line 30, whereby potentiometer 27 is automaticallyadjusted with adjustment of potentiometer 24, 25 and regulates the speedof the traversing drive motor accordingly. For example if the anemometer18 and the discharge end of conveyor 12 reach a spot where the burdenhas unduly high permeability, the potentiometer arm 25 moves clockwiseto restore balance in the control circuit. Potentiometer 27 is adjustedto increase the field strength of motor 15 and thus reduce the speed,whereby the discharge end of the conveyor dwells over this spot. Thereverse action occurs when the discharge end of the conveyor reaches aspot of low permeability. In feed devices which employ more than onetraversing drive motor (for example De Vaney Patent No. 2,834,484), thepotentiometer 27 can automatically be connected in the eld circuit ofthe appropriate motor through suitable relays, or else each motor can beequipped with its own potentiometer.

I have observed that the combustion zone of the furnace remains moreaccurately at the desired location when feeding is controlled inaccordance with permeability than with either the stockline profile orthe gas temperature. The difficulty with a control based on prole isthat the usual balls are not uniform and some tend to compact.Consequently there is no direct relation between the depth of burden andits permeability. I have found it is questionable whether temperaturevaries predictably with permeability.

While I have shown and described only a single embodiment of myinvention, it is apparent that modifications may arise. Therefore, I donot wish to be limited to the disclosure set forth but only by the scopeof the appended claims.

I claim:

1. In a shaft furnace which includes a feeder adapted to delivermaterial to the top of the furnace, a traversing drive for said feeder,and a speed control device for said drive, the combination therewith ofan apparatus for adjusting said speed control device comprising meansfor measuring the velocity of combustion gases passing through thefurnace burden adjacent the spot where the feeder is deliveringmaterial, separate means for measuring the gas temperature atapproximately the same spot, computing means operatively connected withsaid velocity measuring means and said temperature measuring means fordetermining the gas velocity at a standard temperature and therebyproviding an indication of the relative permeability of the burden to owof gases below this spot, and means operatively connecting saidcomputing means with said speed control device to increase the feed rateover spots of relatively high permeability and decrease the feed rateover spots of relatively low permeability.

2. A method of controlling feed to a shaft furnace to which materialfeeds from a traversing feeder, said method comprising measuring thevelocity of combustion gases passing through the burden adjacent thespot where the feeder is delivering material, developing a first voltageproportionate to the velocity measurement, separately measuring thetemperature of the combustion gases at approximately the same spot,developing a second voltage proportionate to the absolute temperaturemeasurement, balancing said first voltage against said second voltage toobtain an indication of the gas velocity at a standard temperature andthus of the relative permeability of the burden to flow `of gases belowthis spot, and varying the rate of traverse in accordance with saidindication to increase the feed rate over spots of relatively highpermeability and decrease the rate over spots of relatively lowpermeability.

References Cited in the file of this patent UNITED STATES PATENTS2,175,541 Probert Oct. l0, 1939 2,306,811 Kennedy Dec. 29, 19422,310,924 Becker Feb. 16, 1943 2,711,837 Henry et al Iune 28, 19552,739,800 Sisco Mar. 27, 1956 2,752,231 Bearer June 26, 1956

